GENEVA - The World Health Organization warned Friday that the annual production of swine flu vaccines is expected to fall well short of the 4.9 billion doses that it had earlier forecast.

Production "will be substantially less than 4.9 billion" doses, WHO spokesman Gregory Hartl told journalists.

Some 25 pharmaceutical laboratories had indicated that weekly production is lower than 94 million doses currently, he said, adding that current clinical trials indicate that a single dose is sufficient to offer immunity against the A(H1N1) virus.

In May, the WHO had forecast a weekly output of 94.3 million doses if full scale vaccine production was launched.

The shortfall was also highlighted in a statement issued by WHO chief Margaret Chan, who said that "current supplies of pandemic vaccine are inadequate for a world population in which virtually everyone is susceptible to infection by a new and readily contagious virus."

The WHO said the global swine flu death toll has reached 3,486, up 281 from a week ago.

In its weekly data published on its website, the UN health agency said the number of deaths since the A(H1N1) virus was uncovered in April rose by 281 from 3,205 a week ago.

The Americas region continued to post the highest death toll, at 2,625.

Asia-Pacific reported 620 fatalities, while Europe recorded at least 140 deaths.

In the Middle East, 61 people succumbed to the virus while in Africa, 40 people died from it.

The WHO observed that flu activity was "above the seasonal baseline" in the United States. France and Japan, meanwhile, have reported that the flu has reached epidemic levels.

Transmission is also rife in the Central and South America and Asia, said the WHO, while in the temperate regions of the Southern Hemisphere, such as Australia and South Africa, flu activity is declining.